This invention relates to a light-sensitive coating solution, more particularly to a light-sensitive coating solution, which gives a light-sensitive liquid improved in odor, low in toxicity and yet excellent in storability, and is also suitable for preparation of a light-sensitive lithographic printing plate improved in press life and dye remaining.
A light-sensitive lithographic printing plate is prepared by dissolving a light-sensitive composition in an appropriate solvent, coating the solution onto a support and drying the coating. In the prior art, during preparation of such light-sensitive lithographic printing plate, as the solvent for dissolving the light-sensitive composition, various solvents have been employed. For example, glycol ethers such as methyl cellosolve (ethylene glycol monomethyl ether), ethyl cellosolve, etc. have been primarily employed.
However, these coating solvents have the problem of strong toxicity during preparation of light-sensitive printing plates, and also have strong odor, with unpleasant feeling as undesirable in working environment. Further, when a light-sensitive composition is coated onto a support by use of a solvent as mentioned above, coatability is poor, generating frequently coating irregularity such as streak irregularity, pinhole, etc., thus involving a problem such that the value as commercial product may be impaired.
Use of a propylene glycol type compound as the solvent for light-sensitive coating liquid is disclosed in Japanese Unexamined Patent Publications Nos. 6648/1986, 14652/1987, etc., but the light-sensitive printing plate obtained by use of such propylene glycol type compound is poor in storability and improvement of this point has been desired.
Further, ester compounds of propylene glycols, etc. used as the coating solvent are improved in odor, toxicity and coatability as compared with the solvents of the prior art such as methyl cellosolve, ethyl cellosolve, etc., but they cannot be said to be satisfactory. For example, 3-methoxybutyl acetate as described in Japanese Unexamined Patent Publication No. 5237/1987, propylene glycol monoalkyl ether acetate in Japanese Unexamined Patent Publication No. 7837/1986 are improved in odor and toxicity, but not only storability of the light-sensitive coating liquid is impaired, but also said compound undergoes hydrolysis because of having acetate structure through the influence by the moisture mixed as the impurity into the light-sensitive liquid or absorption of the moisture in the air, whereby acetic acid is liberated. Due to the liberated acetic acid, drawbacks are seen such that dye remaining is generated on the printing plate after development, and that the press life of the light-sensitive lithographic plate is inferior. Here, dye remaining refers to the phenomenon that, when an image is developed after exposure, the organic dye contained in the light-sensitive composition is attached onto the non-image and streak portion of the printing plate obtained to color the plate. The dye remaining cause problems of difficulty in identification of the image and streak portion from the non-image and streak portion and lowering of layout proof property.